1. Field of the Invention
The present invention relates to communication of one or more data signal streams over a wideband space-time multipath channel, and more particularly to the decomposition and selection for use of one or more sub-channels within the multipath channel.
2. Description of Related Art
The use of wireless communications has grown significantly over the past several years. With it the need to make better utilization of the available spectrum, which is allocated for use in wireless communications, has similarly grown.
In order to support multiple private two-way communications, the available spectrum is generally divided into a plurality of minimally and/or non-interfering sub-channels which are then dynamically allocated between users on a per request basis. Several techniques have been used to improve the utilization of the available spectrum, including improvements in frequency division, signal modulation, and spatial division.
Improvements in frequency division techniques have enabled a greater number of subchannels to be defined in the allotted spectrum by allowing the available frequency to be divided into narrower distinct slices or frequency bands. Improvements in signal modulation techniques including signal compression, time division multiplexing and spread spectrum techniques, such as code division multiple access, have enabled enhancements in both signal quality and channel capacity. Improvements in spatial division techniques which have traditionally included creating localized transmission areas, or cells, and other techniques for geographically restricting signal transmissions, have enabled frequency to be reused in geographically distinct and non-adjacent areas.
More recently spatial division techniques have begun to take advantage of inherent constructive and destructive interfering signal patterns between similar signals originating from or received by multiple spaced apart antennas to more narrowly define a signal region between which a signal is being transmitted or received. In this way signal patterns can be defined in such a way so as to focus a signal transmission within a select portion of a given geographical area by maximizing the strength of the signal directed toward an intended recipient, while minimizing the strength of the signal directed toward non-intended recipients for which the signal might create unwanted interference.
In addition to inherent constructive and destructive interfering signal patterns between signals originating from or received by multiple spaced apart transmitting and receiving antennas, constructive and destructive interfering signal patterns are also created by signals which travel between a transmitter and receiver via multiple signal paths. Multiple signal paths can result from signals which reflect off of one or more structures located between a particular transmitter and receiver as the signal radiates outward. In many instances the reflection of a signal can cause that portion of a signal's energy to be deflected in a manner so as to never be received by the receiver. In other instances a portion of the signal's energy could reflect off of one or more interfering surfaces and be redirected back towards the receiver. Regardless, various portions of a signal often reach their destination via one of a couple of different signal paths. A signal reaching its destination along different paths will often result in the different components of the signal arriving at a different angle and/or arriving at a different time.
In the past, the reception of the same signal at different times was generally destructive in nature and seen as another source of noise known as inter-symbol interference Inter-symbol interference resulting from reception of the same signal at different times due to signal propagation along different paths, generally created a limit on the rate at which data symbols could be transmitted. However more recent techniques have recognized that this inter-symbol interference if accounted for could also be used to enhance signal transmissions, once the transmission characteristics between the two points are known. One such technique includes the use of space-time beamformer technology.
However one of the complications associated with implementing a spatially distinct transmission which constructively combines the multipath signaling characteristics is the amount of computational resources required to compute the transmission requirements and reception requirements for establishing such a geographically discriminating communication connection. The amount of computational resources required for maintaining a spatially distinct transmission is further complicated by the fact that in many wireless communication applications, the transmitter and the receiver are in motion with respect to one another, and/or the objects against which the signal is being reflected are moving with respect to the transmitter and/or the receiver. Consequently, the transmission requirements and reception requirements may need to be recalculated or updated to take into account the continuously changing environment within which the desired communications are taking place, thereby making even greater demands upon the computational resources available for maintaining the quality of communications.
It would therefore be desirable to provide a method for managing the usage of a space-time channel and a channel state processing unit, which reduces the computational resources required for maintaining a spatially distinct transmission including those which make use of space-time beamformer technology.
These and other objects, features, and advantages of this invention are evident from the following description of a preferred embodiment of the present invention, with reference to the accompanying drawings.